This invention is directed generally to the field of oil well drilling and equipment therefor. As more drilling activity is being undertaken in the field in remote locations, including both onshore and offshore drilling, and especially in those instances in offshore drilling where floating vessels are desirable for deep water drilling, the automation of the pipe handling apparatus becomes more desirable, both to reduce the amount of manual labor associated with handling of pipe, and to reduce the expense associated with the requirement of providing laborers. Floating vessels are inherently unstable and may have a rig or derrick constructed on a barge or ship. In derricks mounted upon a stable platform, such as an onshore drilling platform or offshore drilling platform where the platform is anchored to the earth, the automated handling of pipe is also advantageous from the standpoint of reducing the amount of physical labor required and from the standpoint of improving the safety conditions associated with the drilling of wells.
The drill pipe and drill collar handling equipment associated with this invention have been previously available. One type of such equipment is that disclosed in Turner, U.S. Pat. No. 3,561,811; and Turner, U.S. Pat. No. 3,768,663. The drill pipe and drill collar handling equipment is of the type wherein the pipe or drill collars may be positioned quickly and accurately for placing in the well hole, or may be stacked or racked in such a manner that the pipe is held in a position away from the center of the derrick in a stable condition.
In handling the pipe or drill collars, ordinarily the sections are coupled into what is termed "stands" made up of several sections or pipe lengths for handling purposes. It is customary to work a stand of three sections of pipe or drill collars, which stand must be from time to time racked in a position away from the center of the derrick so as to be out of the way of the drilling operations, but readily available to be picked up and moved to a position for connection to the drill string. Such requirements of racking the stands away from the center of the derrick and retrieving them from their racked position, for example, occurs when the drill string is being removed for changing of the drill bit, and is then reinserted into the well hole for continuation of the drilling process. Such removal and reinsertion of the drill string is commonly referred to as round tripping.